Semiconductor elements nowadays are developing toward the trend of smaller line width and higher integrated density. When the minimum line width of an integrated circuit is decreased below 0.25 μm, the time delay (RC delay) caused by the resistance of the metal wire itself and the spurious capacitance of the dielectric layer has become a crucial influence on the operation rate of the elements. Therefore, in order to increase the operation rate of the elements, currently copper metal wires have been gradually adopted in high-level processing below 0.13 μm to replace the traditional aluminum-copper alloy wires.
The application of chemical mechanical planarization technology in the copper metal wire processing may not only overcome the problem of patterns being difficult to define due to the difficulty of copper metal etching, but also form a plane with global planarity upon polishing, so that the multilayer wire processing may be easily carried out. The principle of chemical mechanical planarization is that mechanical wear is produced on the wafer surface by combining polishing particles in a polishing slurry with chemical aids, whereby the high site of the uneven surface has a high removal rate due to high pressure while the low site of the uneven surface has a low removal rate due to low pressure, and thereby the purpose of global planarity can be achieved.
Large quantities of fine polishing particles and chemical aids in the polishing slurry and the scraps peeled during polishing may attach to the chip surface during polishing of the chemical mechanical planarization. In general, the common contaminants found on the chips after polishing are metal ions, organic compounds and polishing particles and the like. If there is no effective cleaning procedure to remove the above-described contaminants, the subsequent processing will be affected, and the yield and the reliability of the elements will be decreased. Therefore, the cleaning processing after CMP polishing has become a crucial technology to determine whether CMP can be successfully applied in semiconductor processing.
In the polishing slurry used in copper processing, benzotriazole (BTA) and its derivatives and ascorbic acid are often employed as a corrosion inhibitor. In the contaminants found on the wafers after polishing in the copper processing, organic residues such as BTA, etc. are the most difficult to remove, mainly because the BTA particles are bonded on the copper wires by chemical adsorption. Physical removal methods such as static repulsive force, ultrasonic vibration and scrubbing with a polyvinyl alcohol (PVA) brush etc., are traditionally used, but it is not easy to obtain a good cleaning effect.
Traditional inter layer/metal dielectric and W plugs that have been treated by chemical mechanical planarization are usually cleaned using ammonia solution and/or fluorine-containing compounds, but the above solutions are not suitable for the wafers of copper metal wires. The ammonia solution will unevenly corrode the surface of copper metal, resulting in coarsening. The fluorine-containing compounds will not only coarsen the copper surface but also cost more in terms of human safety protection and waste solution treatment in order to avoid doing harm to human health and to the environment.
A polishing composition that can effectively remove tantalum metal from a substrate is disclosed in Ina et al., U.S. Pat. No. 6,139,763, which consists of polishing particles, an oxidant that can oxidize tantalum metal, a reducer that can reduce tantalum oxide (such as oxalic acid) and water. This polishing composition can further comprise piperazine (a nitrogen-containing heterocyclic organic base). According to Ina et al.'s teaching, the piperazine can be used on the surface of the copper layer during polishing to prevent the formation of surface impairment, such as recesses, dishing or erosion, which also can protect the polishing surface so as to achieve a mirror-like surface. However, the use of the piperazine in an aqueous cleaning solution employed in the post chemical mechanical planarization in the copper processing is not taught or suggested by Ina et al.
A method of removing chemical residues from a surface of a metal or dielectric layer is disclosed in Small, U.S. Pat. No. 6,546,939 (Taiwan Patent No. 396202), wherein an aqueous composition with a pH between 3.5 and 7 is placed in contact with the metal or dielectric layer for a period of time sufficient to remove the chemical residues. This aqueous composition comprises an organic acid having mono-, bi- or trifunctional groups, a buffering amount of a base of quaternary amine, ammonium hydroxide, hydroxylamine, hydroxylamine salt or hydrazine salt, and a choline hydroxide.
A cleaning agent is disclosed in Small et al., U.S. Pat. No. 6,498,131. The cleaning agent consists of a nonionic surfactant, amines, quaternary amines and a surface retention agent selected from ethylene glycol, propylene glycol, polyethylene oxide and mixtures thereof, and is used to clean the residues of the chemical mechanical planarization processing.
A cleaning agent is disclosed in Naghshineh et al., U.S. Pat. No. 6,492,308. The cleaning agent consists of tetraalkylammonium hydroxide, polar organic amine and a corrosion inhibitor, and is used to clean a copper-containing integrated circuit.
A cleaning agent is disclosed in Nam, U.S. Pat. No. 5,863,344. The cleaning agent consists of tetramethylammonium hydroxide, acetic acid and water, and is used to clean semiconductor elements, wherein the volume ratio of acetic acid to tetramethylammonium hydroxide is preferably 1 to about 50.
A method of cleaning a semiconductor substrate with copper wires on its surface is disclosed in Masahiko et al., U.S. Pat. No. 6,716,803. The cleaning agent used in this method comprises a surfactant and a nitrogen-containing alkaline substance.
A cleaning agent is disclosed in Ward et al., U.S. Pat. No. 5,988,186. The cleaning agent consists of a water-soluble polar solvent, an organic amine and a benzene ring corrosion inhibitor, and is used to remove organic and inorganic substances.
A tetraalkylammonium hydroxide and/or a surfactant and/or a corrosion inhibitor are used as the components of the cleaning solution in the prior art as described above. Tetraalkylammonium hydroxides have a high volatility (a vapor pressure of 18 mm Hg at a temperature of 20° C.), high toxicity and strong odour. If it is not handled appropriately, it will cause damage to humans and the environment. The cleaning effect of the cleaning composition can be enhanced by way of adding the surfactant or changing the surface electrical property of the contaminant and/or the substrate, but this cannot act on contaminants produced by chemical adsorption. The corrosion inhibitor can protect the surface of copper metal during cleaning to avoid the excessive corrosion of the copper metal surface induced by the chemical substances in the cleaning composition. However, the corrosion inhibitor itself may remain on the surface of copper metal after cleaning, resulting in organic residues.
Therefore, the prior art as described above cannot meet the requirements for a cleaning solution used in post chemical mechanical planarization in copper processing in the industry. There is still a desire for an aqueous cleaning composition useful for post chemical mechanical planarization in the copper processing. This ideal composition would be one which is not highly volatile, has no odour, doesn't remain on the wafers after cleaning, and can effectively remove the residual contaminants from the surfaces of the copper process chips that have been treated by chemical mechanical planarization and provide the copper metal wires with a better surface roughness.